The present invention is related generally to time-of-use meters and, more particularly, to a time-of-use meter which stores and responds to a plurality of cyclic dates in a manner which reduces required memory storage capacity.
Electric utility companies provide electricity for their consumers and charge those consumers according to the amount of electrical energy, measured in kilowatt hours, used during a particular period of time. Electric utility watt-hour meters are used to measure the amount of electrical power used by the consumer. By multiplying the number of kilowatt hours by the charging rate per kilowatt hour, the electric utility can determine the total bill that the consumer must pay for the usage of electric power during a particular billing period.
In recent years, providers of electric power have begun to implement multiple charging rates which can vary depending on the specific time when the electric energy is consumed. For example, some watt-hour meters are designed to record a consumer's peak electrical demand. Based partially on this peak demand, the customers billing rate is then determined. For example, U.S. Pat. No. 3,406,338 which issued on Oct. 15, 1968 to Benbow discloses a maximum demand device with a clutch that has an adjustable time and U.S. Pat. No. 3,805,154 which issued on Apr. 16, 1974 to Halstead et al. discloses an improved interval timing mechanism for a maximum demand meter. U.S. Pat. No. 3,913,014 which issued on Oct. 14, 1975 to Halstead et al. discloses a demand meter for on-peak maximum demand metering and U.S. Pat. No. 4,147,983 which issued on Apr. 3, 1979 to Adams et al. discloses a remote meter reading maximum KW demand meter. An on-peak watt hour demand meter having compensation for disc loading variations is disclosed in U.S. Pat. No. 4,156,184 which issued on May 22, 1979 to Benbow.
Rates can also vary as a function of the day of the week, season of the year or time of the day when electrical energy is consumed. Also, electrical energy usage billing rates can be set to different values for week days, weekends and holidays. Electric utility meters of this type are known to those skilled in the art as time-of-day or time-of-use meters. For example, U.S. Pat. No. 4,364,009 which issued on Dec. 14, 1982 to Halstead et al. discloses an improved clutch mechanism for time-of-day watt hour metering registers and U.S. Pat. No. 4,307,341 issued on Dec. 22, 1981 to Benbow et al. discloses an improved clutch mechanism for time-of-day meter registers.
In order to properly function as a time-of-use meter, the electric utility watt-hour meter must be provided with some means for determining the actual time of day, day of year and season. A time-of-use meter must also be able to recognize week days, weekends, holidays and season changes. Therefore, there are generally a plurality of events which can be predicted to occur during each year of use of the time-of-use meter that must be recognized by it. Although the exact number of such events can be expected to vary from utility to utility, there are approximately sixteen yearly events which the time-of-use meter must be able to recognize. For example, in a typical application, ten holiday dates, four season change dates and two dates on which daylight savings time is changed must be recognized by the time-of-use meter. Therefore, besides time-of-day rate changes, the time-of-use meter must be capable of implementing rate changes approximately sixteen times each year.
Since a time-of-use meter typically comprises a computing means, such as a microprocessor or microcomputer, it has the capability of maintaining a time keeping program which, essentially, maintains a calendar and a clock within its memory storage medium. These calendar and clock programs generally maintain data regarding the hour, minute and second of each day along with information that represents the day of the year, month, day of the month, number of days in each particular month and the year. The program would employ an algorithm that accounts for the effect of leap years and the fact that different months comprise different number of days. The computing means is able, according to known algorithms, to derive most of this information by knowing the current year and day of the year. Of course, in order to determine the day of the year at any particular time, the computing means would employ a clock program that updates the hours, minutes and seconds. The clock program is responsive to a stream of timing pulses which have a known frequency. In most typical applications, clock times are a function of a 60 hertz stream of timing pulses which is readily available in most applications.
Since electric utility watt-hour meters are, by their nature, relatively small as compared to most computer based systems, space which is available for the computing means of a time-of-use meter is severely limited. Therefore, the microprocessor, or microcomputer, along with its peripheral memory devices, must also be limited in size. Although recent advancements in the field of electronics have made available relatively large memory storage capacities in relatively small components or chips, the size of the computing means and peripheral memory devices remains a concern. For this reason, and also to reduce cost, it is beneficial to minimize the usage of computer memory as much as possible.
Prior to its initial use, a time-of-use meter must be provided with information concerning cyclical events for which a response is necessary. These cyclic events, such as the typical sixteen events described above must be known by the time-of-use meter so that it can constantly compare the current day of the year to the day of the year of each cyclic event to properly change the billing rate when required. Furthermore, electric utility companies prefer to avoid the need to reprogram their watt-hour meters on a frequent schedule.
Therefore, it is advantageous to preprogram the time-of-use meters for a significant number of years extending from its initial installation. The actual number of years for which a time-of-use meter is programmed is a function both of the desires of the electric utility companies and available memory capacity of the computing means and its associated peripheral memory devices. Some time-of-use meters are preprogrammed to contain the cyclic event date for five or more years, with some time-of-use meters being programmed for up to twenty year periods that follow the initial installation and programming.
Time-of-use meters known to those skilled in the art are, at the present time, programmed to include each individual event that is expected to occur during this preselected period of time. In other words, if a time-of-use meter is programmed for a period of twenty years and each year has sixteen cyclic dates to be remembered, the memory devices of the time-of-use meter would contain 320 individual cyclic event identifiers. Depending on the coding method that is used, the storage of 320 event dates can require 320 or more sixteen bit words of memory capacity with each word comprising 12 or 16 bits. Since, as discussed above, the available space within a time-of-use meter is limited, it is advantageous to provide the time-of-use meter with a more efficient means for remembering these multiple cyclic events over long periods of time. The present invention provides such a time-of-use meter.